Note: Descriptions are shown in the official language in which they were submitted.
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Cementitious Board Manufacture
This invention relates to the manufacture of cementitious board in which a
slurry
of cementitious material, commonly gypsum plaster, is deposited between two
facing lining sheets and formed to a desired width and thickness prior to
setting
and drying. The process is normally carried out continuously and at high
linear
speed.
To manufacture gypsum board an aqueous slurry of calcined gypsum (calcium
sulphate hemihydrate) is continuously spread between upper and lower paper
sheets. The product formed is then continuously conveyed on a moving belt
until
the slurry has set. The strip or sheet is then dried until the excess water in
the
gypsum board has evaporated. In the production of gypsum wallboard it is
known to add various substances to the slurry to enhance the production
process
or the board itself. For example it is usual to lighten the weight of the
slurry by
incorporating foaming agents to provide a degree of aeration which lowers the
density of the final wallboard.
It is also known to decrease the setting time of the calcined gypsum slurry by
incorporating gypsum set accelerators. Freshly ground gypsum (also known as a
gypsum set accelerator) has a relatively short shelf life. The loss of
acceleration
efficiency of conventional accelerator materials is also exacerbated when the
accelerator is exposed to heat and/or moisture.
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To combat this loss of efficiency it is known to coat the accelerator
particles with,
for example, sugar or a surfactant. .
Accordingly, there is a need for a gypsum set accelerator or method of
accelerating the set time of the gypsum slurry which alleviates the
aforementioned problems.
According to the present invention there is provided a method for accelerating
the setting reaction of calcium sulphate hemihydrateand water comprising
mixing
water and calcium sulphate hemihydrateto produce a slurry, adding an
accelerator to said mixture and applying ultrasonic energy to said mixture.
The ultrasonic energy may be applied for a time of less than 10 seconds.
The accelerator may be hydrated calcium sulphate.
The accelerator may be a chemical accelerator.
The chemical accelerator may be potassium sulphate (K2SO4).
The slurry may be formed within a mixer and deposited via a mixer outlet onto
paper so as to form gypsum plasterboard, said paper being located on a
conveyor.
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The ultrasonic energy may be applied to the slurry when the slurry is located
in
the mixer outlet.
The ultrasonic energy may be applied to the slurry once it is deposited on the
paper conveyor.
The ultrasonic energy may be applied using a radial shaped ultrasonic horn
positioned at the exit mouth of the mixer outlet.
The ultrasonic energy may be applied directly to the slurry in the mixer.
The ultrasonic energy may be applied directly to the slurry in the mixer via
probes
inserted into the slurry contained within the mixer.
The ultrasonic energy may also be applied via the rotor in the mixer.
Also according to the present invention there is provided apparatus for
manufacturing gypsum wall board comprising a mixer for combining calcium
sulphate hemihydrate and water, a mixer outlet for depositing the gypsum
slurry
onto paper mounted onto a conveyor, wherein said mixer outlet comprises
means for supplying ultrasonic energy to the slurry as it passes through said
mixer outlet.
Said mixer outlet may comprise a tubular shaped ultrasonic horn.
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Advantageously the application of ultrasonic energy together with a known
accelerator provided a decreased setting time and therefore a more efficient
plasterboard manufacturing process. The application of ultrasonic accelerator
in
to the mixer has also surprisingly alleviated material build up in the mixer.
This is
caused by the vibration produced by the application of ultrasonic energy to
the
mixer. In
particular the combination of the use of ultrasonic energy in
combination with a known gypsum accelerator has provided surprisingly goods
results with the amount of particulate or chemical accelerators needed being
reduced.
Embodiments of the invention will now be described with reference to the
accompanying drawings in which:
Figure 1 is a fragmentary diagrammatical view of a longitudinal section of a
gypsum board manufacturing line.
Figure 2 is an example of a shape of a mixer outlet according to an embodiment
of the present invention.
Figure 3 is a diagrammatic view of a mixer outlet in the shape of a radial
horn
according to a further embodiment of the present invention.
Figure 4 is a diagrammatical section of a mixer with ultrasonic probes
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Figure 5 is a diagrammatical section of a mixer with an ultrasonic rotor
according
to a further embodiment of the invention
Referring to figure 1 a first layer of paper 12 is fed from a roll 14 onto a
conveyor
or belt 16. A storage mixer 18 contains slurry of calcium sulphate hemi
hydrate
and water. This storage mixer 18 is provided with an outlet 20 connected to a
conduit 22. A meter is connected to said conduit 22 for measuring and
controlling the amount of stucco fed through the conduit 22.
Additives are added to the storage mixer 18. Such additives may comprise
retarders (e.g. proteins, organic acids), viscosity modifying agents (e.g.
superplasticisers), anti-burning agents, boric acid, water-resisting chemicals
(e.g. polysiloxanes, wax emulsions), glass fibres, fire-resistance enhancers
(e.g.
vermiculite, clays and/or fumed silica), polymeric compounds (e.g. PVA, PVOH)
and other conventional additives imparted in known quantities to facilitate
manufacturing such as starch.
The storage mixer 18 is provided with an outlet 20 to deliver its combined
contents in the form of slurry onto the paper 12.
This slurry mixture is then delivered through an outlet pipe 22 onto the paper
12
provided on the moving belt 16.
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An additive such as starch is added to the slurry stream 24 in the mixer and a
further layer of paper 26 is provided over its upper surface from a roll 28.
The
slurry if therefore sandwiched between two sheets of paper or cardboard 12 and
26. These two sheets become the facing of the resultant gypsum board.
The thickness of the resultant board is controlled by a forming station 30 and
the
board is subsequently prepared by employing appropriate mechanical devices to
cut or score fold and glue the overlapping edges of the paper cover sheets 12,
26. Additional guides maintain board thickness and width as the setting slurry
travels on the moving conveyor belt. The board panels are cut and delivered to
dryers to dry the plasterboard.
In the current embodiment of this invention, the conduit 22 may be replaced by
a
ring shaped radial horn through which the slurry may be fed to the slurry
stream
24 during transit through the conduit the ultrasonic energy may be delivered.
Referring to figure 2, the conduit 22 may be constructed in the form of a
metallic
ultrasonic radial horn with outer metallic tubing 40 and inner bore 42. The
slurry
24 passes through the conduit 22 where ultrasonic energy is imparted as it
forms
the slurry stream on the paper 12.
Advantageously the use of ultrasonic energy applied to the gypsum slurry
accelerates the setting time of the gypsum by causing accelerated
crystallisation.
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It is understood that when the amount of ultrasonic energy applied to the
gypsum
slurry exceeds the natural forces holding together the molecules, cavitation
occurs.
The implosion of the cavitation bubbles produces short lived hot spots within
the
slurry. The collapse of some of the bubbles within the slurry enable
nucleation
sites to occur thus allowing accelerated crystallisation.
This has the added advantage of making the slurry outlet nozzle a self
cleaning
delivery unit due the vibration produced by the ultrasonic energy. The
vibrations
at the mixer outlet also allow the slurry to be spread evenly across the
moving
conveyor.
In one embodiment of this invention, the conduit 22 may be replaced by a wide
mouthed tubular ultrasonic horn through which the slurry may be fed to the
slurry
stream 24 and during transit through the conduit the ultrasonic energy may be
delivered.
Referring to figure 3, the conduit 22 may be constructed in the form of a
metallic
ultrasonic radial horn with tubular outer metallic tubing 50 connected by some
means to a conical section 52 thereby forming a wide mouthed slurry output
bore
54. The slurry 24 passes through the conduit 22 where ultrasonic energy is
imparted as it forms the slurry stream on the paper 12. Also advantageously by
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=
8
using a wide mouthed design of ultrasonic horn as the mixer outlet the slurry
stream
on the paper 12 may be more uniformly distributed and less reliant on the use
of
additional mechanical vibration apparatus.
Referring now to figure 4 a pair of ultrasonic probes 52a, 54a could
alternatively be
inserted into the mixer chamber 18 itself. The probes 52a and 54a
advantageously
act as a method for preventing mixer blockage by providing vibration to the
slurry
mixture.
Referring to figure 5 the rotor 53 of the mixer is itself provided with
ultrasonic energy
via a generator 57. The rotor is essentially a conventional rotor but
additionally
provided with ultrasonic energy which it can impart to the gypsum slurry
mixture fed
into the mixer chamber 18.
The following example results further illustrate the present invention but
should not
be construed as limiting its scope.
With reference to the examples:
= The slurry was made using stucco of different water gauges including 70,
and
90 wt % of stucco (no additives) to obtain different viscosities.
= The different slurries with the different water gauges were insonated
with an
ultrasonic probe (at a fixed frequency of 20kHz) for different intervals,
including 2, 3, 5, 10, 15 and 20 seconds.
= The set time for each insonation was measured using a Vicat set test.
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= To determine the effect of foam on the insonation, different slurries
with
different addition levels of foam was tested in the same manner as
explained above for the unfoamed slurries. In this case the water gauges
were kept constant and the foam addition level altered.
= Both sets of examples (using unfoamed and foamed slurries) were
repeated using different ultrasonic probes with different power outputs,
(1kW and 1.5 kW).
= The examples were repeated with the use of ultrasound in combination
with particulate accelerator, Ground Mineral Nansa (GMN) and a chemical
accelerator, potassium sulphate.
Example 1
Prisms were made using 1000g of stucco at three different water gauges of 70,
80 and 90 wt% of stucco. Ultrasonic energy was applied to the slurry for 3, 5
and
seconds using an ultrasonic probe with a power output of lkW. A large high-
speed blender was used to mix the stucco and water for a dispersion time of 5
seconds. The water used remained at a constant temperature of 40 C. No foam
was added to the slurry in this case.
Table 1
Difference Average
Insonation Water Initial Set Final Set Average
in Set
Compressive
Time Gauge Times Times Density
Time Strength
(seconds) (wt%) (minutes) (minutes) (minutes) (kg/m3) (MPa)
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0 70 8.10 9.45 1080 12.7
10 70 4.50 7.00 -2.45 1078 14.6
0 80 8.00 9.20 1004 10.4
3 80 6.56 7.57 -2.03 994 10.9
0 80 8.35 10.10 995 9.9
5 80 6.20 8.20 -2.30 990 10.3
0 80 8.15 9.45 986 9.6
10 80 5.50 7.13 -2.32 969 10.9
0 90 8.00 9.50 913 8.2
3 90 6.57 8.00 -1.50 921 8.6
0 90 8.30 9.30 959 8.0
5 90 6.38 7.40 -2.30 927 9.5
0 90 8.30 10.15 912 8.4
10 90 6.37 8.00 -2.15 917 8.8
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Example 2
Tests were carried out to determine the effect of ultrasonic acceleration on
foamed slurries. Prisms were made using 1000g of stucco with a water gauge of
90 wt% of stucco. A foam generator was used to produce the foam to be added
to the stucco blend. The foam generator was set to have an airflow rate of 2.5
l/min, foam flow rate of 0.25 l/min and a foam concentration of 0.3%. To
produce
the slurry mix, a large blender was used on low speed for a total dispersion
time
of 10 seconds. The 1kW ultrasonic probe was used at insonation times of 3, 5
and 10 seconds to accelerate the set of the gypsum slurry.
The stucco and water was mixed in a large batch mixer for 3 seconds before the
foam was added to the blend and mixed for a further 7 seconds to produce
samples 1 and 2. In the case of samples 3 and 4, stucco was mixed with water
for 3 seconds before the foam was added and mixed for a further 4 seconds.
Result Table 2
Difference Average
Insonation Initial Set Final Set Average
in Set Compressive
Time Times Times Density
Time Strength
(seconds) (minutes) (minutes) (minutes) (kg/m3) (MPa)
0 11.00 13.00 828 5.19
3 9.27 10.20 -3.20 812 4.20
0 11.45 13.15 723 2.99
3 10.58 11.50 -2.05 607 2.17
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0 8.30 10.30 776 4.62
6.15 7.15 -3.15 755 2.35
0 10.15 12.00 781 4.88
5 7.20 8.20 -4.20 715 3.82
0 12.15 13.00 735 3.88
8.36 9.30 -4.10 714 2.65
0 10.15 12.00 807 4.71
10 7.16 7.50 -4.50 753 2.72
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Example 3
To compare the set times obtained with particulate accelerator as opposed to
solely ultrasonic energy, prisms were made to test the effect of ultrasound on
particulate accelerator (GMN). In this case, no foam was added and a water
gauge of 90wr/o of stucco with a water temperature 40 C was used. A large
high-speed blender was used to mix the stucco and the GMN with water for a 5
second dispersion time. GMN was hand mixed into dry stucco powder for 30
seconds before making the slurry in the blender.
Result Table 3
Difference Average
Insonation Initial Set Final Set Average
`YoG M N in Set
Compressive
Time Time Time Density
Time Strength
(seconds) (wt%) (minutes) (minutes) (min) (kg/m3) (MPa)
control 0 0.5 3.00 3.45 905.89
8.33
3 0.5 2.12 3.00 -0.45 852.52
4.23
0.5 2.24 3.00 -0.45 815.20 5.65
0.5 1.50 2.48 -1.37 829.94 4.66
control 0 0.1 5.30 6.15 904.24
8.63
3 0.1 4.30 5.30 -1.25 880.61
8.55
5 0.1 3.45 4.40 -2.15 876.04
7.32
10 0.1 3.50 4.54 -2.01 892.16
7.37
control 0 0 8.50 11.00 903.85
6.92
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0 4.30 5.20 -6.20 921.21 11.00
Example 4
Non-foamed slurry was insonated using a higher power probe that could draw
1.5kW compared with 1kW power (that the previous probe was capable of).
1000g of stucco with a water gauge of 90wr/o (water temperature of 40 C) was
again mixed in a high-speed blender for 5 seconds to produce the samples.
Table 4
Difference in Set
Insonation Time Initial Set Time Final Set Time
Times
(seconds) (minutes) (minutes) (minutes)
0 10.30
2 7.30 10.00 -0.30
0 7.45 9.25
4.30 6.20 -3.05
0 8.00 9.15
4.15 5.30 -4.25
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Example 5
Non-foamed samples with two addition levels (0.06 and 0.1wt%) of potassium
sulphate (chemical accelerator) were insonated using a higher powered probe
(1.5kW) for different intervals to determine whether ultrasonic cavitation
could be
used in conjunction with potassium sulphate to further accelerate the set time
of
gypsum slurry.
Table 5
Potassiu Initial Final Differenc
Insonatio Densit Compressiv
m Set Set e in Set
n Time y e Strength
Sulphate Time Time Time
(seconds (minutes (minutes (kg/m3
(wt%) (minutes) (MPa)
) ) ) )
0 0 7.56 10.56 927.06 8.68
2 0 7.00 9.15 -1.41 919.40 8.38
0 0.06 7.12 8.12 914.61 8.31
2 0.06 4.40 6.59 -1.53 909.86 8.72
0 0.06 5.47 7.38 910.10 8.03
3 0.06 4.06 6.39 -1.39 908.97 8.18
0 0.06 5.59 8.20 910.81 8.42
10 0.06 5.25 6.20 -2.00 916.53 9.08
0 0.1 6.18 7.56 922.73 8.42
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2 0.1 5.25 6.37 -1.19 914.02 8.53
0 0.1 4.58 7.06 917.63 8.22
3 0.1 4.58 5.50 -1.56 921.49 8.67
0 0.1 5.57 7.39 902.00 8.32
0.1 4.35 5.30 -2.09 900.25 8.72
As seen in table 5, the application of ultrasound energy in combination with a
chemical accelerator (potassium sulphate) produces a substantial increase in
set
time. This particular combination of ultrasound energy and chemical
accelerator
has been found to be more effective in reducing the setting time of the gypsum
slurry than either method on its own.
Table 6 is a list of results obtained from on plant' trials using ultrasound
according to the present invention to accelerate the setting of gypsum.
Table Of Results For Plant Trials Usinq Ultrasound To Accelerate The
Settino Of Gvosum Products
Description Final Avg Difference
Date Trial set final set (minutes) Notes
10/05/0 Control 1 3.20 3.15 -1.10
5
Control 3.20
Control 3.20
Control 3.10
Control 3.00
Control 3.20
10/05/0 Uls on line radial horn 2 2.50 2.45
5 circumference only
Uls on line radial horn 2.40
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Icircumference only 1 1 1 1
10/05/0 Control 2a 3.20 3.30 -0.20
Control 3.40
Uls on line radial horn 3.10 3.10
circumference only (Natural
Gypsum)
10/05/0 Control 4 3.50 3.42
5
Control 3.20
Control 3.55
Uls through centre of radial horn 3.00 2.78 -1.04
into skip
Uls through centre of radial horn 2.55
into skip
Uls 90 degree to flow underneath 3.15 3.15 -0.27
into skip
11/05/0 Control 5 3.10 2.87
5
Control 2.50
Control 3.00
11/05/0 Control 6 3.50 3.50 0.28
5
Uls with centre blocked same 4.00 3.78 NB. Too much
direction as flow into skip foam present
uls with centre blocked same 3.55 NB. Too much
direction as flow into skip foam present
Control 3.35 3.45 -1.28
Control 3.55
uls with centre blocked same 3.05 2.58 Half stream
direction as flow into skip sonicated
uls with centre blocked same 2.30 Full stream
direction as flow into skip sonicated
uls with centre blocked same 2.50
direction as flow into skip
uls with centre blocked same 2.45
direction as flow into skip
11/05/0 Control 7 4.30 4.25 -1.37
5
Control 4.20
Uls through horn (added water) 4.20 ignore Too much water
into skip
Uls through horn 3.25 3.28
Uls through horn into skip 3.20
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lUls through horn into skip 1 13.40 1 1
11/05/0 Control - Normal recipe into skip 8 3.25 3.18
Control - Normal recipe into skip 3.10
Control - Normal recipe into skip 3.20
Control -no GMN or retarder 3.55 3.55 -0.50 Suspect
some
GMN still present
Uls under the horn same direction 3.10 3.05
as flow (no GMN or retarder)
Date Description Trial Final Avg
Difference
set final set (minutes)
11/05/0 Uls under the horn same direction 3.00
5 as flow into skip (no GMN or
retarder)
Control - Flushed out all GMN and 3.40 3.40 -1.13
no retarder
Uls under the horn same direction 2.25 2.28
as flow into skip (no GMN or
retarder)
Uls under the horn same direction 2.30
as flow into skip (no GMN or
retarder)
Control - no GMN but with retarder 3.50 3.50 -0.50
Uls under the horn same direction 3.50 3.00
as flow (no GMN with retarder)
Uls under the horn same direction 2.50
as flow into skip (no GMN but with
retarder)
11/05/0 Control - No GMN or retarder 9 3.40 3.67 -1.11
5
Control - No GMN or retarder 3.10
Control - No GMN or retarder 2.45
Control - No GMN or retarder 4.45
Control - No GMN or retarder 4.45
Control - No GMN or retarder 4.10
Control - No GMN or retarder 4.15
Control - No GMN or retarder 3.25
Uls underneath the horn 90 3.25 2.96
degree to flow (no GMN or
retarder)
Uls underneath the horn 90 2.45
degree to flow (no GMN or
retarder) into skip
Uls underneath the horn 90 3.15
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degree to flow (no GMN or
retarder) into skip
Uls underneath the horn 90 3.00
degree to flow (no GMN or
retarder) into skip
11/05/0 Control - No GMN or retarder 10 4.10 4.10 -1.33
Uls flat head horn (no GMN or 3.25 3.18 Slurry
bouncing off
retarder) 50% of power Amp. working face.
Uls flat head horn into skip (no 3.10
GMN or retarder) 50% of power
Amp.
Table 7 is a summary table of results of set time, achieved during the plant
trials.
Date Control Treatment Difference in
Set Time
(minutes)
10/05/05 Normal recipe Ultrasound on-line radial horn, -0.41
circumference only.
11/05/05 Normal recipe Ultrasound on-line radial horn, -0.18
circumference only.
11/05/05 Normal recipe Ultrasound through the centre of the -1.37
radial horn.
11/05/05 No Ultrasound on-line radial horn, -1.18
accelerator no circumference only.
retarder.
11/05/05 No Ultrasound on-line radial horn, -0.50
accelerator circumference only.
but with
retarder.
11/05/05 No Ultrasound flat head horn, 50% of -1.33
accelerator no power.
retarder.
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Summary Plot Of Difference In Set Times Achieved With the Use Of
Ultrasound On Plant Trials
Ultrasonic acceleration cove line trial 100505 and 110505
5.00 ____________________________________________________ i
Uls through horn Uls under the horn same
direction as flow (no GMN with
4.00 - Uls with centre blocked same direction as
direction as ilow \ '4µi' Uls under the horn same
retarder)
` %,,,,,,,õ \ Uls flat
head horn (no GMN or
Uls on line radial horn direction al \µµ no GMN or si 'µ,..',õV
retardeir) 50% oi power Amp.
m
circumterence r r )
, = = , .µµt \\
3.00 -
\ FS= control
=ultrasonic
.,,,%, =.=.. i W
-iia;
---, - Difference in set times
-' 2.00 -
W
. ti .,,,%, =.=.. i
,...%,
.,,,%, =.=.. i
lE 1.00 -
.,,,%, =.=.. i W 'if
ir) 1
Co
.
0.00 ' I I
00 Ã 6
E
-,,i
'di
.c
-1. - 6 cu
o
c
m
:IT)
2.00 ______________________________________________________
Trial number
Data Regarding Density Reduction With The Use of Ultrasound
The plots below emphasise the density reduction properties of using
ultrasound.
Comparing all the controls with the ultrasonically treated samples shows that
all
of them have a lower density than the controls. The treated samples had a
corresponding strength with regard to density. The ultrasound did not have a
detrimental effect on strength but simply reduced the density. The treated
samples present the same proportional change in strength with density as seen
from the control samples.
The density reducing property of ultrasound is another beneficial effect.
Ultrasound could therefore also be used to aerate the slurry, allowing a
reduction
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in water gauge or foam usage. The reduction in water gauge is of greater
economic benefit, since it would mean a reduction on the energy usage. The use
of ultrasound would mean the benefit of mechanically aerating the slurry and
achieving the same product densities with reduced quantity of water or foam.
Compressive stress data for ultrasonic cove line trial.
5.00
4.50 u:,c =
4.00
l'71' 3.50
o_
u) 3.00 , = = control
a compressive stress
2.50
Linear (compressive stress)
.(7) 2.00 õ , , - Linear
(control)
8- 1.50
1.00
0.50
0.00 µ\\'µ
550.00 600.00 650.00 700.00 750.00
Density (Kg/m 3)
CA 02 62 6 6 61 2 0 0 8-0 4-1 8
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Flex 3 point bend
2.50 .................................................
BC.
Sec *act 8C! =
2.00
.1?440. acb *
2
ft 3 II. =
1.50 = control Flex
µ,3cf =
::.,:mommomionomonnionommommomm ultrasound flex
cc
............................................................. Power
(ultrasound flex)
ie = :.:aUggOgnMaUggOgnaMaUgOgnMaUgg0
CO 1.00 -
Power (control Flex)
z
3
2
0.50
I111111111111111111111111111111111111111111111111111111111111111111111111111111
1111111111111111111111111111111111111111111111111111111111111111111111111111111
1111111111111111111111111111111111111111111111111111111111111111111111111111111
1111111111111111111111111111111111111111111111111111111111111111111111111111111
1111111111111111111111111111111111111111111111111111111111111111111111111111111
1111111111111111111111111111
,..............................................................................
...............................................................................
...............................................................................
...............................................................................
...............................................................................
............................
0.00 _________________________________________________
550.00 570.00 590.00 610.00 630.00 650.00 670.00 690.00 710.00 730.00
Density (kg/m3)
